The moves themselves don't deal that much damage, they're just pretty fast and can easily string several hits.
Nair and dair could do a lot but it was really hard getting them to land all their hits. If they get any easier to land perfectly a damage
nerf doesn't seem unlikely.
He's fairly good at raising damage in the air for sure, but he's no Ness.
Nair is frame 5, does 17%, easily connects 6 hits or more (that's at least 12%) unless you purposefully cancel it early, few characters in the game have a viable response to Nair shield pressure (Nair -> Jab). It also strings into his other moves like Nair, Dair or Jab (10%).
Dair is frame 4, does 20%, you're pretty much guaranteed to land at least 3 hits, can be footstooled into itself at least three times (that's a little under 60% total), strings into Nair, Jab etc. at earlier %s, and at higher percents sets up into a Dtilt lock -> Usmash/Fsmash kill which works on Bowser starting at about 105% and Jigglypuff at 60%.
It's honestly not that hard to connect all the hitboxes. Just look at PF, Mekos or the japanese Lucases. I did it all the time against other people on WiFi, and even if you miss a few you still get a good damage output.
Regardless of whatever optimizations they do with Nair/Dair's hitboxes, Lucas will be getting nerfed in damage output, it's not a good idea letting him run around with 40% comboes.